Catechin is reported to possess an α-amylase-activity-inhibiting effect as one of its physiological properties (see Patent Document 1). In order for such a physiological effect to materialize, a large amount of catechin needs to be ingested more conveniently, so there has been a strong demand for a method by which a high concentration of the catechin can be added to a beverage.
Employed as one of such methods is to add the catechin in a dissolved form to a beverage by making use of a tea extract such as a concentrate of green tea extract (Patent Document 2). However, depending on the kind of the beverage to which the catechin is to be added in the high concentration by this method, for example, when catechin is added to a black tea extract solution or a carbonated beverage, the residual bitterness and astringency intrinsic to the caffeine and the green tea are known to considerably impair the commercial value of the beverage.
It has been known for years that an application of tannase treatment to an extract solution of fermented tea such as black tea, can inhibit a suspension, in other words, the formation of tea cream when cooled at low temperatures. According to a method that subjects the green tea extract solution to tannase treatment as disclosed in Patent Document 3, it is possible to reduce the percentage of gallate forms, which are a cause of bitterness, in the non-polymer catechins. Further, as methods for removing impurities such as caffeine from tea extracts, adsorption methods (Patent Documents 4-6), an extraction method (Patent Document 7) and the like are known.    Patent Document 1: JP-A-03-133928    Patent Document 2: JP-A-59-219384    Patent Document 3: JP-A-2004-321105    Patent Document 4: JP-A-2004-222719    Patent Document 5: JP-A-08-109178    Patent Document 6: JP-A-2002-335911    Patent Document 7: JP-A-01-289447